Drilling rig operators often employ the use of Measurement-While-Drilling (MWD) and Logging-While-Drilling (LWD) tools and services during drilling operations, to measure and/or log various conditions within the borehole and/or the rock formations surrounding the borehole. MWD/LWD tools utilize a variety of sensors to sample and aggregate digital values for real-time transmission to the surface during drilling operations. The transmission scheme and channel medium may vary. For example, they may include Mud Pulse Telemetry (MPT) through water and drilling mud, Electro-Magnetic-Telemetry (EMT) through rock formations, and Acoustic Telemetry (AT) via the drill-string. Each scheme typically employs some form of modulation (e.g. Orthogonal Frequency Division Multiplexed (OFDM), or Direct Sequence Spread Spectrum (DSSS)) to increase the reliability of communication through the associated medium.
When either OFDM or DSSS modulation are used, the transmit peak-to-average-power-ratio (PAPR) is often poor (i.e., relatively high), as compared to other processes, even though error rates may be improved. As a result, a more expensive transmitter power amplifier, with a higher dynamic range, is often used to maintain a desired level of reliability within a given communication system.
During drilling operations, the driller will often pump fluids, e.g. “drilling mud” or water, into the borehole via a set of pumps (typically positive displacement pumps) through the drill string and out the drill bit. The fluids return to the surface through the annulus (the space between the drill-string and borehole wall). This drilling mud is quite ubiquitous in drilling operations, and due to costs or formation constraints, it is often the media of choice for transmitting information—using mud pulse telemetry (MPT). However, the data rates provided by MPT are relatively low when compared to other mechanisms of data transport.